1. Field of the Invention
The present invention relates to a returnable IC tray having an antistatic property and a high heat-resistant property, excellent in mechanical characteristics, free from warpage and deformation, and reusable, and a resin composition for giving the same.
2. Description of the Prior Art
Trays for heat treatment of IC are used in the field of electric and electronic engineering. Especially for conveying, or drying for dehydrating IC parts, trays which were produced by molding a composition consisting essentially of a polyphenylene ether resin, a polyether imide resin or a polysulfone resin have heretofore been used. Regarding the heat resistance property of these IC trays for dehydrating IC parts, the trays being resistive at a temperature of below 200.degree. C. were satisfactory.
Recently, however, use of trays under higher temperature, for example, the trays for a reflow soldering step which is to be effected at a temperature higher than 200.degree. C. has been required. In such use, compositions consisting essentially of a polyphenylene ether resin, a polyether imide resin or a polysulfone resin could not be practicable, because their heat-resistant property was not sufficient. Therefore, in the treatment of IC parts at a temperature higher than 200.degree. C., IC trays made of metal (aluminum) were used. However, metallic IC trays are defective in that they can not be produced in industrial-scale injection molding, are difficult to be processed, expensive, and heavier than the resinous trays. Accordingly, resinous IC trays which are light in weight, capable of being produced at low costs and capable of being substitutable for such use of metallic ones have been desired. In such a situation, use of thermoplastic polyimide resins which have the highest heat-resistant property among thermoplastic resins may be taken into consideration. In such a use, in general, since there exist many cases where the surface resistivity of the molded parts should be controlled in order to make the molded parts antistatic, it is important to improve this characteristic of the molded parts.
In general, to control the surface resistivity of thermoplastic resins, employed is a technique of adding conductive carbon thereto by kneading them together. In this technique, however, there happen many cases in which the carbon would drop off from the formed resin molded parts when the molded parts are contacted with and rubbed against electronic parts (in other words, the molded parts are worn out at the contacted area), which resulted in the dropped-out carbon would penetrating into the insulating area of the electronic parts and thereby interfering with the insulation in the area. Thus, in some cases, use of carbon is often problematic. Specifically, for reuse of IC trays, it is necessary that they are not deformed and worn out while they are repeatedly reused.
On the other hand, there exists a technique of adding carbon fiber to thermoplastic resins by kneading them together, which could be free from the problem noted above, however, is problematic in another respect in that the orientation of carbon fiber, if occurred, in the resin molded parts induces anisotropic shrinkage which might cause warpage of the molded parts.
In addition, for IC trays and other molded parts having complicated forms, it is relatively difficult to release them from molds, and if they are released by force from molds, they will be warped.
Moreover, it is further desired to use IC trays at an ultra-high temperature of 250.degree. C. or higher. However, no resin materials for IC trays capable of being used at such a high temperature have heretofore been known.
Finally, the mechanical characteristics of IC trays which are obtained by molding a composition consisting essentially of a polyphenylene ether resin, a polyetherimide resin or a polysulfone resin are worsened while the trays are used for a long period of time. Specifically, the long-term heat-resistant property of these IC trays is poor. For example, IC trays of polyphenylene ether could hardly be reused at 150.degree. C. Even if could possible, they could not be reused 30 times. Given such a situation, desired are reusable, returnable, resinous IC trays which are capable of being reused even at a high temperatures of 200.degree. C. or higher (of course, are also capable of being reused at temperatures lower than 200.degree. C.).